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Effect of propranolol on growth hormone response to GH releasing hormone (GHRH 1–44) in the dog
SHORT COMMUNICATIONS Research in Veterinary Science 1992, 52, 110-112
Effect of propranolol on growth hormone response to cn releasing hormone (¢;rIRH 1-44) in the dog A REGNIER, Ecole Nationale VOtOrinaire, 31076 Toulouse Cedex, France, L. BRET, CJF Inserm 88.01, FacultO de MOdecine Purpan, 31073 Toulouse Cedex, France, M. MORRE, Sanofi Recherche, 31035 Toulouse Cedex, France
The present study was undertaken to examine whether ~-adrenergic blockade with propranolol might influence and make less variable the growth hormone (GH) response to exogenous GH releasing hormone (GtlRH) 1-44 in the dog. On four separate occasions eighi healthy beagles, one to two years old, randomly received either propranolol (40 ~tg kg-1 intravenously) or an equivalent volume of saline, 30 minutes before either Gram 1-44 (1 ~tg kg -1 intravenously) or vehicle was injected. After propranolol alone, GH secretion did not differ from saline (area under the curve [AUC]: 649"5 _+ 128-3 v 633"2 _+ 87"7 ng min m1-1, respectively). GI-I~ alone elicited a significant increase in GH secretion (AUC : 1230"5 +- 210"5 ng mill m1-1) with a peak concentration of 16"7 _+ 4-8 ng m1-1. When GmtH was injected after propranolol the mean peak (59"1 _+ 14"7 ng ml-l) and secretory area (AUC: 2631"0+_474"4 ng min m1-1) were greater than those observed after GHRHalone. However, from a clinical point of view propranolol pretreatment does not modify the great individual variability of the GH response to GHRH.
E N D O G E N O U S growth hormone (GH) secretion from the anterior pituitary is controlled primarily by the release of two hypothalamic neurohormones, one stimulatory, that is, GH releasing hormone (GHRH), and one inhibitory, that is, somatostatin (SRIF). The former specifically stimulates GH synthesis and release while the latter suppresses basal GH release and inhibits GH secretion induced by provocative agents (Frohman and Jansson 1986, Buonomo and Baile 1990). The secretion of these hypothalamic hormones is controlled, in turn, by a number of stimulatory and inhibitory neurotransmitters. Implicated among these are the catecholamines (MOller et al 1987). In the healthy dog, human synthetic GHRH 1-44 is able to stimulate GH secretion, but the increase in plasma GH elicited by the neuropeptide is quite variable among the subjects (Abribat et a11989). Consequently, a blunted or absent response to a dose of GHRH does not exclude normal pituitary function in the dog, limiting the diagnostic usefulness of GHRH testing. Animal and human studies have clearly shown that [3-adrenergic blockade potentiates the somatotrope
response to exogenous GHRHand reduces the interindividual heterogeneity of the GH response, improving the reliability of this provocative test (Chihara et al 1984, 1985). In order to investigate whether pretreatment with a [3-adrenergic antagonist, that is, propranolol, may affect the GH response to GHRHin the dog, making it less variable, the present work was undertaken. Eight healthy beagles (three females, five males) one to two years old and weighing 8 to 15 kg were used. The dogs were housed in individual cages and acclimatised to their quarters for three weeks before beginning the study. All experiments were carried out in conscious animals, after an overnight fast, starting between 08.30 and 09.00. Four experimental protocols were performed on each dog in a random design separated each time by at least three days. Experiments consisted of giving, by slow intravenous injection, either 40 ~tg kg-1 propranolol hydrochloride (Avlocardyl; ICI Pharma) or an equivalent volume of saline, 30 minutes before either 1 ~tg kg-1 GHRH 1-44 (Synthetic hGRF 144; Sanofi Recherche) or vehicle for GHRH (1 ml 0-9 per cent saline) was administered intravenously as a bolus dose. Blood samples were collected in EDTA vacuum tubes 30 and 15 minutes before, immediately before and five, 15, 30, 45, 60, 90 and 120 minutes after the injection of either GHRHor vehicle. The samples were centrifuged for 10 minutes at 4°C and plasma frozen at -20°C until assayed for GH. Plasma canine GH was measured in duplicate by a homologous radioimmunoassay (Pituitary Hormones and Antisera Center, Torrance) method described previously (Abribat et al 1989). The GH responses were expressed either as absolute concentrations (ng m1-1) or as areas under the response curve (AUC, ng min ml-l) calculated by trapezoidal integration. Numerical results are given as mean + SEM. Statistical analysis of the data was carried out using non-parametric analysis of variance followed by the multiple comparison test of Tukey (Sokal and Rohlf 1981). Significance of a statistical test was considered to be 0.05 or less. Propranolol and GHRH given alone or in combination did not produce an~ clinically apparent side effects 110
Propranolol-GHRH testing in the dog Saline
111
GHRH or vehicle
or
4500
_
A
60 - p r o p r a n o l o l
1.2_ E 40
15oo
20
1
o -30-15
0
15
30 45 Time (min)
60
90
120
FtG 1 : Mean (+ SEM) plasma GH concentrations in eight healthy dogs after (40 pg kg-1) propranolol or the same volume of saline given intravenously at -30 minutes followed by 1 /.tg kg -1 GHRHor vehicle intravenously. J ~ Saline +GHRH vehicle, 0-------0 Propranolol +GHRH vehicle. Saline +GHRH. ~ Propranolol +GHRH
1
2
3
4 5 Dog number
6
7
8
FIG 2: Individual secretory GH responses to either GHRH (1 /J.g kg -1) or vehicle, given intravenously 30 minutes after administration of propranolol (40 t.tg kg -1) or an equivalent volume of saline. • Saline -I-GHRHvehicle, • Propranolol + GHRH vehicle. ~ Saline + GHRH. Propranolol +GHRH
The results of this study support a previous obserin any of the dogs. Basal hormone concentrations at -30, -15 and 0 minutes time points did not differ sig- v a t i o n (Abribat et al 1989) that human GHRH is able nificantly between the dogs pretreated with propra-~ to induce highly variable GH responses in healthy dogs. nolol and those given the same volume o f saline (Fig Such considerable individual variations in G H responses 1). There was no Significant change in basal levels of to GHRH have been observed in man with both GHRH GH after GHRH vehicle, in both dogs pretreated with 1-44 and 1-29 (Rosenthal et al 1983, Gelato et al 1984, propranolol and those pretreated with saline (Fig 1): Mazza et al 1989). It is generally thought that the variConsequently, the AUC was not significantly different ability of the GH response to intravenous GHRH is due between the two groups (saline pretreatment/GHRH to fluctuations of the somatostatinergic tone. The vehicle: 633.2 _+ 87.7 ng rain ml 1; propranolol pre- administration of exogenous G H R H during a period of treatment/GHRH vehicle: 649.5 + 128:3 ng min mkl)~ predominant hypothalamic SRIF secretion would When GHRH was administered after saline a significant induce a low GH response and vice versa (Devesa et increase in plasma GH concentration from baseline was al 1989). Administration of propranolol alone did not observed at five, 15, 30 and 45 minutes. The G H peak affect basal GH release in our dogs. This result is in level of 16.7 + 4.8 ng m k 1 occurred at 15 minutes (Fig line with previous reports in human medicine (Chihara 1). Comparisons of the areas under the G H release et al 1985, Massara et al 1986, Arosio et al 1990), sugcurves revealed that GHRH (AUC: 1230.5 + 210.5 ng gesting that the action of propranolol is not likely to min m1-1) resulted in a significantly greater release of be mediated by stimulation of endogenous GHRH GH than its vehicle. However the effect of GHRH was release. quite variable among the dogs, as demonstrated by These data also indicate that ~-adrenergic blockade comparison of the individual GH secretory responses is able to potentiate the GH response to exogenous (Fig 2). G H R H in the dog. This result is in agreement with preIn dogs pretreated with propranolol, G H R H admin- vious reports in man (Chihara et al 1984, 1985). It is istration led to a significant elevation in mean GH con- generally accepted from these results and others centrations from baseline at five, 15, 30, 45, 60 and (Altszuler et al 1988, Kelijman and Frohman 1989) 90 minutes with a peak level of 59.1 + 14-7 ng m1-1 that the addition of propranolol by decreasing SRIF occurring at 15 minutes (Fig 1). Comparisons of the secretion and thereby removing an inhibitor of GH AUCs revealed that the mean GH secretory response secretion may allow the stimulatory effect of the GH after GHRH was significantly higher in the animals secretagogue. pretreated with propranolol (AUC: 2631.0 + 474"4 ng From a clinical point of view, the dosage of 40 ~tg min m1-1) than in those pretreated with saline. kg -1 propranolol, although enhancing the mean GH However, pretreatment with the drug did not modify response to GHRH, did not abolish the variability of the variability of the individual responses and did not the individual responses and did not prevent the occurpotentiate the GH response to GHRH in two animals rence of a negative response in two of the eight dogs. (dogs 2 and 5) that were also unresponsive to GHRH The dosage of propranolol used in this study was arbialone (Fig 2). trarily chosen midrange between dosages of 20 to 60
112
A. Regnier, L. Bret, M. Morre
lag kg -1 commonly recommended for parenteral administration in the dog (Novotny and Adams 1986). The persisting variability of the GH responses to GHRH after propranolol pretreatment might indicate that a bolus dose of 40 lxg kg-1 propranolol is not sufficient to maximally inhibit hypothalamic SRIF release in the dog. In consequence, further studies are needed to determine the optimal modalities of the combined proprano101-GHRn test that would abolish the possibility of false negative responses in healthy subjects.
Acknowledgements The authors are grateful to Dr A. F. Parlow, for kindly providing the materials for canine GH radioimmunoassay. References ABRIBAT, T , REGNIER, A. & MORRE, M. (1989) Growth hormone response induced by synthetic human growth hormone-releasing factor (1-44) in healthy dogs. Journal of Veterinary Medicine A36, 367-373 ALTSZULER, N., RICHARDSON, S. B. & TWENTE, S. (1988) Adrenergic modulation of growth hormone release. Proceedings of the 70th Annual Meeting of the Endocrine Society, New Orleans. pl19 AROSIO, M., BAZZONI, N., BOCHICCIO, D., PALMIERI, E., NAVA, C. & FAGLIA, G. (1990) Effects of propranolol on Gla responsiveness to repeated Ga-releasing hormone stimulations in normal subjects. Acta Endocrinologica 122, 735-739 BUONOMO, F. C. & BAILE, C. A. (1990) The neurophysiological regulation of growth hormone secretion. Domestic Animal Endocrinology 7, 435-450 CHIHARA, K., MINAMITANI, N., KAJI, H., KODAMA, H., KITA, T. & FUJITA, T. (1984) Noradrenergic modulations of human pancreatic growth hormone-releasing factor (hp GHRF l44)-induced growth hormone release in conscious male rabbits: involvement of endogenous somatostatin. Endocrinology 114, 14021406 CHIHARA, K., KODAMA, H., KAJI, H., KITA, T., KASHIO, Y., OKIMURA, Y., ABE, H. & FUJITA, T. (1985) Augmentation by propranolol of growth-hormone releasing hormone (I-44)-NH 2induced growth hormone release in normal short and normal children. Journal of Clinical Endocrinology and Metabolism 61, 229233
DEVESA, J., LIMA, L., LOIS, N., FRAGA, C., LECHUGA, M. J., ARCE, V. & TRESGUERRE, J. A. F. (1989) Reasons fc,r the variability in growth hormone (GH) responses to GHRHchallenge: the endogenous hypothalamic-somatotrophrhythm (nsg). Clinical Endocrinology 30, 367-377 FROHMAN, L. A. & JANSSON, J. (1986) Growth hormone-releasing hormone. Endocrine Reviews 7, 223-253 GELATO, M. C., PESCOVITZ, O. H., CASSORLA F., LORIAUX, D. k & MERRIAM, G. R. (1984) Dose response relationships for the effects of growth hormone-releasing factor 1-44 NH2 in young adult men and women. Journal of Clinical Endocrinology and. Metabolism 59, 197-201 KELI JMAN, M. & FROHMAN, A. (1989) [3-adrenergicmodulation of growth hormone (GH) autofeedback on sleep-associated and pharmacologically induced OH secretion. Journal of Clinical Endocrinology and Metabolism 69, 1187-1194 MASSARA, F., GHIGO, E., MAZZA, E., CAREDDU, D., POGLIANO, G. F., MULLER, E. E., MOLINATTI, G. M. & CAMANNI, F. (1986) Effects of various adrenergic agonists and antagonists on the growth hormone releasing factor-induced growth response in normal subjects. Journal of Endocrinological Investigation 8, (supplement 3), 51 MAZZA, E., GHIGO, E., GOFFI, S., PROCOPIO, M., IMPERIALE, E., ARVAT, E., BELLONE, J., BOGHEN, M. F., MULLER, E. E. & CAMANNI, F. (1989) Effect of thepotentiation of cholinergic activity on the variability in individual GH response to Gn-releasing hormone. Journal of Endocrinological Investigation 12, 795-798 MULLER, E. E., CELLA, S. G., CAMANINI, F., GHIGO, E., LOCATELLI, V., COCCHI, D., PINTOR, C. & MASSARA, F. (1987) Growth hormone secretion: neuropharmaeological aspects. In Growth Hormone, Growth Factors a~d Acromegaly. Eds D. K. Lgdecke and G. Tolls. New-York, Raven Press. pp55-66 NOVOTNY, M. J. & ADAMS, H. R. (1986) New perspectives in cardiology: recent advances in antiarrhythmic drug therapy. Journal of the American Veterinary Medical Association 189, 533-539 ROSENTHAL, S. M., SCHRIOK, E. A., KAPLAN, S. L., GUILLEMIN, R. & GRUMBACH, M. M. (1983) Synthetic human pancreas growth hormone-releasingfactor (hp GRF 1-44 NH2) stimdates growth hormone secretion in normal men. Journal of Clinical Endocrinology and Metabolism 57, 677-679 SOKAL, R. R. & ROHLF, F. J. (1981) Biometry. The Principles and Practice of Statistics in Biological Research. 2nd edn. NewYork, W. H. Freeman. pp 208-270
Received March 20, 1991 Accepted August 6, 1991
112
Effect of propranolol on growth hormone response to cn releasing hormone (¢;rIRH 1-44) in the dog A REGNIER, Ecole Nationale VOtOrinaire, 31076 Toulouse Cedex, France, L. BRET, CJF Inserm 88.01, FacultO de MOdecine Purpan, 31073 Toulouse Cedex, France, M. MORRE, Sanofi Recherche, 31035 Toulouse Cedex, France
The present study was undertaken to examine whether ~-adrenergic blockade with propranolol might influence and make less variable the growth hormone (GH) response to exogenous GH releasing hormone (GtlRH) 1-44 in the dog. On four separate occasions eighi healthy beagles, one to two years old, randomly received either propranolol (40 ~tg kg-1 intravenously) or an equivalent volume of saline, 30 minutes before either Gram 1-44 (1 ~tg kg -1 intravenously) or vehicle was injected. After propranolol alone, GH secretion did not differ from saline (area under the curve [AUC]: 649"5 _+ 128-3 v 633"2 _+ 87"7 ng min m1-1, respectively). GI-I~ alone elicited a significant increase in GH secretion (AUC : 1230"5 +- 210"5 ng mill m1-1) with a peak concentration of 16"7 _+ 4-8 ng m1-1. When GmtH was injected after propranolol the mean peak (59"1 _+ 14"7 ng ml-l) and secretory area (AUC: 2631"0+_474"4 ng min m1-1) were greater than those observed after GHRHalone. However, from a clinical point of view propranolol pretreatment does not modify the great individual variability of the GH response to GHRH.
E N D O G E N O U S growth hormone (GH) secretion from the anterior pituitary is controlled primarily by the release of two hypothalamic neurohormones, one stimulatory, that is, GH releasing hormone (GHRH), and one inhibitory, that is, somatostatin (SRIF). The former specifically stimulates GH synthesis and release while the latter suppresses basal GH release and inhibits GH secretion induced by provocative agents (Frohman and Jansson 1986, Buonomo and Baile 1990). The secretion of these hypothalamic hormones is controlled, in turn, by a number of stimulatory and inhibitory neurotransmitters. Implicated among these are the catecholamines (MOller et al 1987). In the healthy dog, human synthetic GHRH 1-44 is able to stimulate GH secretion, but the increase in plasma GH elicited by the neuropeptide is quite variable among the subjects (Abribat et a11989). Consequently, a blunted or absent response to a dose of GHRH does not exclude normal pituitary function in the dog, limiting the diagnostic usefulness of GHRH testing. Animal and human studies have clearly shown that [3-adrenergic blockade potentiates the somatotrope
response to exogenous GHRHand reduces the interindividual heterogeneity of the GH response, improving the reliability of this provocative test (Chihara et al 1984, 1985). In order to investigate whether pretreatment with a [3-adrenergic antagonist, that is, propranolol, may affect the GH response to GHRHin the dog, making it less variable, the present work was undertaken. Eight healthy beagles (three females, five males) one to two years old and weighing 8 to 15 kg were used. The dogs were housed in individual cages and acclimatised to their quarters for three weeks before beginning the study. All experiments were carried out in conscious animals, after an overnight fast, starting between 08.30 and 09.00. Four experimental protocols were performed on each dog in a random design separated each time by at least three days. Experiments consisted of giving, by slow intravenous injection, either 40 ~tg kg-1 propranolol hydrochloride (Avlocardyl; ICI Pharma) or an equivalent volume of saline, 30 minutes before either 1 ~tg kg-1 GHRH 1-44 (Synthetic hGRF 144; Sanofi Recherche) or vehicle for GHRH (1 ml 0-9 per cent saline) was administered intravenously as a bolus dose. Blood samples were collected in EDTA vacuum tubes 30 and 15 minutes before, immediately before and five, 15, 30, 45, 60, 90 and 120 minutes after the injection of either GHRHor vehicle. The samples were centrifuged for 10 minutes at 4°C and plasma frozen at -20°C until assayed for GH. Plasma canine GH was measured in duplicate by a homologous radioimmunoassay (Pituitary Hormones and Antisera Center, Torrance) method described previously (Abribat et al 1989). The GH responses were expressed either as absolute concentrations (ng m1-1) or as areas under the response curve (AUC, ng min ml-l) calculated by trapezoidal integration. Numerical results are given as mean + SEM. Statistical analysis of the data was carried out using non-parametric analysis of variance followed by the multiple comparison test of Tukey (Sokal and Rohlf 1981). Significance of a statistical test was considered to be 0.05 or less. Propranolol and GHRH given alone or in combination did not produce an~ clinically apparent side effects 110
Propranolol-GHRH testing in the dog Saline
111
GHRH or vehicle
or
4500
_
A
60 - p r o p r a n o l o l
1.2_ E 40
15oo
20
1
o -30-15
0
15
30 45 Time (min)
60
90
120
FtG 1 : Mean (+ SEM) plasma GH concentrations in eight healthy dogs after (40 pg kg-1) propranolol or the same volume of saline given intravenously at -30 minutes followed by 1 /.tg kg -1 GHRHor vehicle intravenously. J ~ Saline +GHRH vehicle, 0-------0 Propranolol +GHRH vehicle. Saline +GHRH. ~ Propranolol +GHRH
1
2
3
4 5 Dog number
6
7
8
FIG 2: Individual secretory GH responses to either GHRH (1 /J.g kg -1) or vehicle, given intravenously 30 minutes after administration of propranolol (40 t.tg kg -1) or an equivalent volume of saline. • Saline -I-GHRHvehicle, • Propranolol + GHRH vehicle. ~ Saline + GHRH. Propranolol +GHRH
The results of this study support a previous obserin any of the dogs. Basal hormone concentrations at -30, -15 and 0 minutes time points did not differ sig- v a t i o n (Abribat et al 1989) that human GHRH is able nificantly between the dogs pretreated with propra-~ to induce highly variable GH responses in healthy dogs. nolol and those given the same volume o f saline (Fig Such considerable individual variations in G H responses 1). There was no Significant change in basal levels of to GHRH have been observed in man with both GHRH GH after GHRH vehicle, in both dogs pretreated with 1-44 and 1-29 (Rosenthal et al 1983, Gelato et al 1984, propranolol and those pretreated with saline (Fig 1): Mazza et al 1989). It is generally thought that the variConsequently, the AUC was not significantly different ability of the GH response to intravenous GHRH is due between the two groups (saline pretreatment/GHRH to fluctuations of the somatostatinergic tone. The vehicle: 633.2 _+ 87.7 ng rain ml 1; propranolol pre- administration of exogenous G H R H during a period of treatment/GHRH vehicle: 649.5 + 128:3 ng min mkl)~ predominant hypothalamic SRIF secretion would When GHRH was administered after saline a significant induce a low GH response and vice versa (Devesa et increase in plasma GH concentration from baseline was al 1989). Administration of propranolol alone did not observed at five, 15, 30 and 45 minutes. The G H peak affect basal GH release in our dogs. This result is in level of 16.7 + 4.8 ng m k 1 occurred at 15 minutes (Fig line with previous reports in human medicine (Chihara 1). Comparisons of the areas under the G H release et al 1985, Massara et al 1986, Arosio et al 1990), sugcurves revealed that GHRH (AUC: 1230.5 + 210.5 ng gesting that the action of propranolol is not likely to min m1-1) resulted in a significantly greater release of be mediated by stimulation of endogenous GHRH GH than its vehicle. However the effect of GHRH was release. quite variable among the dogs, as demonstrated by These data also indicate that ~-adrenergic blockade comparison of the individual GH secretory responses is able to potentiate the GH response to exogenous (Fig 2). G H R H in the dog. This result is in agreement with preIn dogs pretreated with propranolol, G H R H admin- vious reports in man (Chihara et al 1984, 1985). It is istration led to a significant elevation in mean GH con- generally accepted from these results and others centrations from baseline at five, 15, 30, 45, 60 and (Altszuler et al 1988, Kelijman and Frohman 1989) 90 minutes with a peak level of 59.1 + 14-7 ng m1-1 that the addition of propranolol by decreasing SRIF occurring at 15 minutes (Fig 1). Comparisons of the secretion and thereby removing an inhibitor of GH AUCs revealed that the mean GH secretory response secretion may allow the stimulatory effect of the GH after GHRH was significantly higher in the animals secretagogue. pretreated with propranolol (AUC: 2631.0 + 474"4 ng From a clinical point of view, the dosage of 40 ~tg min m1-1) than in those pretreated with saline. kg -1 propranolol, although enhancing the mean GH However, pretreatment with the drug did not modify response to GHRH, did not abolish the variability of the variability of the individual responses and did not the individual responses and did not prevent the occurpotentiate the GH response to GHRH in two animals rence of a negative response in two of the eight dogs. (dogs 2 and 5) that were also unresponsive to GHRH The dosage of propranolol used in this study was arbialone (Fig 2). trarily chosen midrange between dosages of 20 to 60
112
A. Regnier, L. Bret, M. Morre
lag kg -1 commonly recommended for parenteral administration in the dog (Novotny and Adams 1986). The persisting variability of the GH responses to GHRH after propranolol pretreatment might indicate that a bolus dose of 40 lxg kg-1 propranolol is not sufficient to maximally inhibit hypothalamic SRIF release in the dog. In consequence, further studies are needed to determine the optimal modalities of the combined proprano101-GHRn test that would abolish the possibility of false negative responses in healthy subjects.
Acknowledgements The authors are grateful to Dr A. F. Parlow, for kindly providing the materials for canine GH radioimmunoassay. References ABRIBAT, T , REGNIER, A. & MORRE, M. (1989) Growth hormone response induced by synthetic human growth hormone-releasing factor (1-44) in healthy dogs. Journal of Veterinary Medicine A36, 367-373 ALTSZULER, N., RICHARDSON, S. B. & TWENTE, S. (1988) Adrenergic modulation of growth hormone release. Proceedings of the 70th Annual Meeting of the Endocrine Society, New Orleans. pl19 AROSIO, M., BAZZONI, N., BOCHICCIO, D., PALMIERI, E., NAVA, C. & FAGLIA, G. (1990) Effects of propranolol on Gla responsiveness to repeated Ga-releasing hormone stimulations in normal subjects. Acta Endocrinologica 122, 735-739 BUONOMO, F. C. & BAILE, C. A. (1990) The neurophysiological regulation of growth hormone secretion. Domestic Animal Endocrinology 7, 435-450 CHIHARA, K., MINAMITANI, N., KAJI, H., KODAMA, H., KITA, T. & FUJITA, T. (1984) Noradrenergic modulations of human pancreatic growth hormone-releasing factor (hp GHRF l44)-induced growth hormone release in conscious male rabbits: involvement of endogenous somatostatin. Endocrinology 114, 14021406 CHIHARA, K., KODAMA, H., KAJI, H., KITA, T., KASHIO, Y., OKIMURA, Y., ABE, H. & FUJITA, T. (1985) Augmentation by propranolol of growth-hormone releasing hormone (I-44)-NH 2induced growth hormone release in normal short and normal children. Journal of Clinical Endocrinology and Metabolism 61, 229233
DEVESA, J., LIMA, L., LOIS, N., FRAGA, C., LECHUGA, M. J., ARCE, V. & TRESGUERRE, J. A. F. (1989) Reasons fc,r the variability in growth hormone (GH) responses to GHRHchallenge: the endogenous hypothalamic-somatotrophrhythm (nsg). Clinical Endocrinology 30, 367-377 FROHMAN, L. A. & JANSSON, J. (1986) Growth hormone-releasing hormone. Endocrine Reviews 7, 223-253 GELATO, M. C., PESCOVITZ, O. H., CASSORLA F., LORIAUX, D. k & MERRIAM, G. R. (1984) Dose response relationships for the effects of growth hormone-releasing factor 1-44 NH2 in young adult men and women. Journal of Clinical Endocrinology and. Metabolism 59, 197-201 KELI JMAN, M. & FROHMAN, A. (1989) [3-adrenergicmodulation of growth hormone (GH) autofeedback on sleep-associated and pharmacologically induced OH secretion. Journal of Clinical Endocrinology and Metabolism 69, 1187-1194 MASSARA, F., GHIGO, E., MAZZA, E., CAREDDU, D., POGLIANO, G. F., MULLER, E. E., MOLINATTI, G. M. & CAMANNI, F. (1986) Effects of various adrenergic agonists and antagonists on the growth hormone releasing factor-induced growth response in normal subjects. Journal of Endocrinological Investigation 8, (supplement 3), 51 MAZZA, E., GHIGO, E., GOFFI, S., PROCOPIO, M., IMPERIALE, E., ARVAT, E., BELLONE, J., BOGHEN, M. F., MULLER, E. E. & CAMANNI, F. (1989) Effect of thepotentiation of cholinergic activity on the variability in individual GH response to Gn-releasing hormone. Journal of Endocrinological Investigation 12, 795-798 MULLER, E. E., CELLA, S. G., CAMANINI, F., GHIGO, E., LOCATELLI, V., COCCHI, D., PINTOR, C. & MASSARA, F. (1987) Growth hormone secretion: neuropharmaeological aspects. In Growth Hormone, Growth Factors a~d Acromegaly. Eds D. K. Lgdecke and G. Tolls. New-York, Raven Press. pp55-66 NOVOTNY, M. J. & ADAMS, H. R. (1986) New perspectives in cardiology: recent advances in antiarrhythmic drug therapy. Journal of the American Veterinary Medical Association 189, 533-539 ROSENTHAL, S. M., SCHRIOK, E. A., KAPLAN, S. L., GUILLEMIN, R. & GRUMBACH, M. M. (1983) Synthetic human pancreas growth hormone-releasingfactor (hp GRF 1-44 NH2) stimdates growth hormone secretion in normal men. Journal of Clinical Endocrinology and Metabolism 57, 677-679 SOKAL, R. R. & ROHLF, F. J. (1981) Biometry. The Principles and Practice of Statistics in Biological Research. 2nd edn. NewYork, W. H. Freeman. pp 208-270
Received March 20, 1991 Accepted August 6, 1991
112